Fuel injection was invented for the diesel or compression ignition engine and in fact is necessary for the proper operation for that type of internal combustion engine. As used in a diesel engine, a fuel injection system is characterized by a mechanically driven pump and distributer which supplies fuel oil under pressure to the individual injection nozzles. The system is remarkably reliable but quite expensive to build and maintain. The otto cycle or spark ignition engine on the other hand has in the past almost exclusively used a carburetor for supplying volatilized fuel to the intake manifold of the engine. While not as reliable as the mechanical fuel injection system of a typical diesel engine, the carburetor is neither expensive to manufacture or maintain. Until the past decade when fuel economy became of increasing importance in the design and operation of automobiles, fuel injection systems for spark ignition engines were to be found generally only on high performance race cars and certain exotic imported automobiles. However, the cycles of limited availability and increasing prices for gasoline have made fuel injection and its advantages of increased fuel economy the fuel induction system of choice for all but a few of the automobiles now being manufactured.
The fuel injection systems which have been developed for modern spark ignition engines have been a compromise in performance and cost of manufacture. While mechanical fuel injection systems are known for spark ignition engines, because of their expense to manufacture and maintain, such systems have not been favored. Instead, the predominate choice is one of the several electronic fuel injection systems that have been recently developed. These systems typically use solenoid injector nozzles which respond to pulses from a microprocessor programmed to properly control the timing and duration of injector opening. Not only are these injector nozzles expensive to manufacture because of the very close tolerances required, they are also difficult to regulate because of differing operating characteristics exhibited by individual nozzles. One attempt to avoid these problems has been the development of so-called throttle body fuel injection which uses only one or at most two injector nozzles in the throttle body of the intake manifold. This is an attempt to combine the advantages of computer controlled solenoid injector nozzles with the economy and simplicity of a carburetor. Unfortunately, this approach compromises the superior fuel distribution characteristic of earlier fuel injection systems that led to their adoption for reasons of the fuel economies these systems were capable of producing.